A. Field of the Invention
The present invention relates to a new and improved system for heating fluids such as water and the like.
B. Description of the Prior Art
There are many prior art systems for heating establishments such as buildings and homes and for providing hot water for the use of the occupants of those buildings or homes. It is desirable in such situations to use energy such as electricity to heat the water during periods when electrical utilities generating equipment is operating below capacity, i.e. "off peak" periods. "Off Peak" operation reduces the cost of electrical energy and increases the efficiency of the system. Such systems typically include tanks within which a fluid such as water is contained. Water temperature is elevated through the use of electrical heating elements to store heat during off peak periods.
Once the temperature of the stored fluid is elevated to the desired level in these systems, working fluid such as water is thermally coupled to the storage tank, raising the temperature of the working fluid, either for heating the building or for hot tap water for the occupant. Examples of such systems are illustrated in U.S. Pat. Nos. 3,422,248, 3,630,275 and 4,143,642 incorporated by reference herein.
Prior art systems such as those listed above, however, include complex piping arrangements and multiple mixing valves. It is desirable to reduce the complexity of the piping system and the number of components while maintaining or increasing the efficiency of the system thereby reducing the cost and increasing the utility to the public.
Typical prior art systems employ heat exchangers for removing heat from the stored fluid to a circulating working fluid. The heat exchangers in the prior art include a plurality of U-shaped tubes mounted in an outer shell defining "tube side" and shell side passages internal of the exchanger. It has been discovered that if these tubes are placed in horizontal planes, only the lower tubes, depending on the flow rate, are required for heating. This horizontal arrangement greatly reduces the amount of steam that must be condensed from the tubes and maintains higher velocity in the tubes thus reducing the build up of materials in the upper tubes not in use at high storage temperatures.
In the past, typical prior art systems experienced difficulty with condensers under low system operating pressures. The difficulty resulted from too much steam being generated for the size of the condensing assembly. It was discovered that the same physical size prior art condenser was more effective if used in combination with horizontally arranged tubes in heat exchangers due to the reduced steam generated by these tubes.
In addition, typical prior art systems include back-up flow condenser units and it has been discovered that due to the reduced steam generated by horizontally arranged tubes, the back-up generated steam is routed to the main condenser and a back-up flow condenser is not required. It is desirable to eliminate the back-up flow condenser in order to eliminate the hammer that usually occurs in such condensers due to transient condensation.